1. Field of the Invention
The present invention relates to a silver halide photographic material and a method of processing it. The present invention is applicable to the production of rapidly processable light-sensitive materials and to their rapid processing. Therefore, the present invention finds utility in X-ray film applications.
2. Description of the Prior Art
The consumption of silver halide photographic materials has been increasing in the past decade and, in order to meet the increased demand of consumers for developing and processing photographic films, more rapid development and processing, or an increased capability of process film within a given period of time, is greatly needed. This tendency is also found in areas where X-ray light-sensitive materials such as medical X-ray films are used. As it is recommended that periodical checkups should be strictly carried out, the number of medical tests currently being conducted is growing rapidly. On the other hand, more items are included these days in clinical testing in order to ensure more accurate diagnoses. Both of these factors have lead to an increase in the number of X-ray images to be taken. In addition, persons who have received check-ups want to know the results as soon as possible. In order to meet these demands in the medical field, not only is it necessary to automate diagnostic procedures (e.g. imaging and film transport) but it is also required to process X-ray films more rapidly.
A common method of reducing the length of the processing time (consisting of development, fixing, washing and drying steps) is to increase the film transport speed. However, if the roller speed is increased in an attempt at reducing the processing time required for processing with a roller transport type automatic processor, several problems occur, such as (a) insufficient densities (ie, decreased sensitivity, contast and maximum density), (b) insufficient fixing, (c) insufficient film washing with water, and (d) insufficient film drying. If fixing and washing are insufficient, the color of the processed film will change during its storage to cause image deterioration.
These problems could be solved by reducing the gelatin content but a film having a lower gelatin content has a tendency to produce a grainy photographic image. In addition, if films are rubbed against each other or against another object, the rubbed portion will produce a higher density than other areas if the film is developed and this phenomenon is generally referred to as "abrasion blackening".
It is therefore required to realize very rapid processing of photographic films without causing any of the problems associated with increased roller speeds or decreased gelatin contents. The term "very rapid processing" as used in this specification means that the total period of time required for the film to be transported from the point where its front end is inserted into an automatic processor and passes through a developer tank, a transit area, a fixing tank, the next transit area, a washing tank, a further transit area, and a drying section to the point where it finally emerges from the last-mentioned section is within the range of from 20 to 60 seconds. The total processing time (sec) may be obtained by dividing the total length (m) of processing line by the line transport speed (m/sec). The time required for the film to pass through the three transit areas is included in the total processing time because, as is well known in the art, substantial processing is regarded to take place in each of these transit areas where the gelatin film is also wetted with the processing solution carried over from the previous step.
Japanese Patent Publication No. 47045/1976 mentions the importance of gelatin content for the purpose of rapid processing but the total processing time including passage through transit areas that is attained by this technique ranges from 60 to 120 seconds, which is longer than is desirable in a truly "very rapid" processing.
Another requirement that should be met by modern photographic materials is high sensitivity. For instance, in the wake of the rapid increasing frequency of medical X-ray testing conducted these days, not only those in the medical field but also public opinion at large sees a strong need to reduce the total dose of X-rays to which a patient is exposed and thus the development of highly sensitive photographic materials which requires lower X-ray doses to produce images that have sharpness even in fine detail is desired.
Many and various techniques are available for achieving sensitization, or providing an increased sensitivity for a given grain size. If an appropriate sensitization technique is employed, it will be possible to achieve a higher sensitivity with the grain size (hence the covering power) being maintained at the same level. Among the sensitization techniques reported so far are included: addition of a development accelerator such as a thioether to the emulsion; supersensitizing a spectrally sensitized silver halide emulsion with an appropriate combination of dyes; and employing improved optical sensitizers. However, these methods do not always provide the intended results when they are applied to high-sensitivity silver halide photographic materials; that is, if silver halide emulsions intended to be used in high-sensitivity silver halide photographic materials are treated by these methods, the materials are liable to experience fogging during storage.
In the field of medical X-ray photography, conventionally used light-sensitive materials of the regular type having a spectral sensitivity up to 450 nm are being replaced by ortho-type materials which have been subjected to orthochromatic sensitization so that they possess sensitivity up to a wavelength of 540-550 nm. These sensitized materials not only have an extended spectral sensitivity region but also display increased sensitivity and hence are effective for the purpose of minimizing potential hazards to human health by reducing the total dose of X-rays. Although dye sensitization is a very useful means of sensitization, many problems still remain unsolved; for instance, the sensitivity that can be attained is highly dependent on the type of specific photographic emulsion used.
It is well known to incorporate indazoles or benzotriazoles in a developing solution as anti-foggants. These compounds have been used as anti-foggants both in black-and-white developers and in color developers. While the use of these compounds as anti-foggants is shown in many patent specifications, three are listed here: U.S. Pat. No. 2,271,229 which describes the use of an indazole-based anti-foggant in both a black-and-white developer and in a color developer; BP No. 1,437,053 which discloses the use of an indazole in an X-ray developer as an anti-foggant; and U.S. Pat. No. 4,172,728 which shows the use of an indazole in a graphic arts developer as an antifoggant. These indazole and benzotriazole compounds are very effective anti-foggants, but they still have the disadvantage of causing a substantial drop in sensitivity.